Fluid coking process



Jufiy 7, 1959 J. w. BROWN 2,893,945

FLUID COKING PRQCESS Filed April 8, 1954 PRODUCT 4 O AROMATIC l 700 E T FLUE GAS CRUDE EP R TOR. 22 I s A A k 6 2s 5 21 FLUID TRANSFER LINE COKER BURNER r TAR 17E SEPARATOR I5 IJ 3o 7 f H P a a AROMATIC a sTEAM TAR STEAM James W. Brown Inventor By K C M Attorney 2,893,946 FLUID COKING PROCESS James W. Brown, Mountainside, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application April 8, 1954, Serial No. 421,786 4 Claims. (Cl. 208-100) This invention relates to the art of pyrolytically upgrading hydrocarbon oils. More particularly, it pertains to a process for coking heavy petroleum oils by contacting such oils under pressure with high temperature particulate solids.

Recently it has been proposed to coke hydrocarbon oils such as petroleum residua by injecting them into a coking vessel containing a fluidized bed of high temperature finely divided solids, e.g., coke, sand, spent catalyst, and the like. In the coking vessel, the oil undergoes pyrolysis in the fluidized bed, evolving lighter hydrocarbons and depositing carbonaceous residue on the solid particles. The necessary heat for the pyrolysis is supplied by circulating a stream of the fluidized solids through an external heater, generally a combustion zone, and back to the coking vessel. This fluid coking process is more fully depicted in co-pending application entitled Fluid Coking of Heavy Hydrocarbons and Apparatus Therefor, Serial No. 375,088, filed August 19, 1953, by Pfeiifer et al.

In conventional fluid coking processes, the overhead products boil up to around 1100 F. and normally show high ash and Conradson carbon content. The products boiling above about 1000 F. may be recycled to the coker to improve the gas oil, but the resulting gas oil is still around 2% Conradson carbon and of borderline quality in ash content. To secure a good catalytic cracking gas oil, it is possible to recycle more of the heavy gas oil or a lighter material, such as 700 F. products, to the coking zone, but the recycle rates are exceedingly high.

In some instances, however, it is desirable to make products boiling entirely below about 700 F., particularly when the coker feed stock is highly aromatic or high in nitrogen content such that the resulting coker gas oil is of exceptionally low value as feed for catalytic cracking.

The present invention makes possible the production of low end point gas oil from a fluid coker without the necessity for recycle of the overhead products.

This invention involves coking an oil at elevated pressures, e.g., 50 p.s.i.g., or above, in such a manner that the heavy gas oil is held in the liquid phase on the fluidized solids in the coker until it pyrolytically decomposes. Thus, only light products escape from the coker and no, or very little, recycle is required.

This invention also involves the feature of continuously withdrawing a side stream of coke from the main coking zone along with adhering liquid oil and introducing it into a high severity thermal cracking and stripping zone. This is advantageous in that build-up of aromatic, refractory gas oil on the particulate coke in the main coking zone is prevented. With this arrangement, it is possible to attain minimumreactor size and to withdraw from the stripping zone an aromatic tar product which, if cracked, would produce mostly coke and gas.

Removal of this aromatic product from a secondary coking stage or thermal cracking and stripping zone States Patent "ice makes possible the direct quenching of the primary coker overhead products with fresh feed. The direct quenching of the coker eflluent with fresh feed is known to be desirable for heat economy, but, in processes previously proposed, results in mixing with the feed a refractory cycle stock which is, preferably, withdrawn.

An object of the present invention is to pyrolytically upgrade heavy petroleum oils. A more specific object is to obtain maximum yields of middle distillate from heavy hydrocarbon oils by coking the oils under pressure utilizing the fluidized solids technique. Another object is to devise a two-stage hydrocarbon oil fluid coking process whereby a maximum yield of hydrocarbons boiling below about 700 F. is obtained without the necessity of recycle.

These and other objects will appear as this discussion proceeds and the attached drawing, forming a part of this specification, is described in detail.

The drawing shows a preferred embodiment of this invention applied to the cracking of a highly aromatic crude to obtain maximum yields of products boiling under 700 F. A main fluid coking vessel is used in conjunction with a secondary coking and stripping zone and a transfer line burner system is used to supply the necessary heat for the pyrolysis. This arrangement is most advantageously used with a crude, such as Coleville crude, that has a large proportion of high boiling, refractory constituents.

Referring to the drawing, a crude, supplied by line 1, such as Coleville crude, is preheated by direct contact with the coker overhead vapors in line 2 and the 700 F. and lighter virgin and thermally cracked products are flashed overhead in a separator 3 and removed by line 4 as product. A more complete separation of product could, of course, be made at this point as desired. The products may be subjected to further processing such as hydrocracking, stabilization, catalytic cracking, blending, etc.

The separator bottoms are fed via line 5 to a fluid coking vessel 6 operated at about 900 F., and 50 p.s.i.g. This high pressure maintains practically all of the 700 F.-|- hydrocarbons in the liquid phase until they crack.

A dense fluidized bed of particulate coke of about 40-800 microns is maintained in the coking vessel by admitting steam or other fluidizing gas at the base of the vessel at a plurality of points, one of which is shown by line 7. The superficial velocity of the ascending steam and hydrocarbon vapors is maintained at about 0.1 to 3 feet per second. The fluidizing stream also serves to strip in the stripping zone 8 hydrocarbons from the coke that is withdrawn as product by line 9. This stripping ;zone is small as it strips only the coke removed as prodnet and does not strip the coke passed to the secondary cracking zone 11.

As an alternate, tail gases from the coker product recovery and separation system or from other refinery operations, such as C and lighter hydrocarbons, may be used as the fluidizing and stripping gas in place of steam. The use of such gases is beneficial in controlling hydrocarbon partial pressures in the reaction zones and in preventing or inhibiting the formation of water emulsions in the product recovery system.

A portion of the fluid bed in coking vessel 6 is continuously removed by line 10 to a thermal cracking and stripping zone 11 to prevent build-up of aromatic and refractory gas oil in the particulate coke. If this gas oil is not removed, the main fluid bed will agglomerate or bog down because of the wetness of the particles unless the feed rate to the coker is greatly reduced.

The stripper 11 is supplied with steam by line 12 and this steam maintains the fluidity of the particulate coke and strips the aromatic hydrocarbons from it.

The stripper temperature is preferably elevated by addition of hot coke from the heater or burner 19 so as to produce the maximum cracking of the aromatics before they are removed. In this way, the temperature of the stripping may be maintained at about 1050 F. by high temperature solids supplied by line 23.

The aromatics removed by the stripper are transferred by line 13 to a tar separator wherein an aromatic tar fraction boiling above about 700 F. is separated and removed by line 15. A portion of the tar may be cooled in heat exchange 24 and recycled by line 25 as reflux.

The remainder of the material from the stripper is sent, via lines 26 and 2, to the product separator 3.

Coke is removed from the lower portion of the stripper by line 17 and conveyed to a combustion zone, e.g., transfer line burner 19, or recycled to the main coking vessel via line 27. An aerating gas, preferably air, is admitted to the vertical riser section of line 17 by line 16 and steam is admitted to line 27 by line 28 to circulate the solids.

A large portion of solids is, preferably, recycled from the stripper to the coker via lines 27 in order that there be a sufliciently high amount of solids circulated to the stripper from the coker through line 10 to carry over the unconverted oil from the coker to the stripper. This feature is particularly desirable when the crude oil has a large proportion of unvaporizable constituents and when the solids are circulated from the burner 19 at a high temperature, say 1500 F. By circulating solids from the stripper to the coker, a major portion of the heat requirements of the coker can be met, because the stripper ll operates at a higher temperature, and only a minor portion of the solids circulated from the burner need be introduced directly into the main coking vessel.

Combustion air is admitted to the base of the burner by line 18. The coke is conveyed through the burner by entrainment at a velocity above about 20 ft./sec., e.g., 60 ft./sec. The air supports a partial combustion of the particles, thereby raising their temperature to about l000-l800 F., e.g., 1200 F.

The gas and entrained solids are transferred from the burner to a solids-gas separator or cyclone 21, wherein the flue gases are separated and removed by line 22. The high temperature solids are conveyed by lines 23 and 24 respectively to the stripper and the fluid coking vessel.

It may be desirable to operate the combustion zone at near atmospheric pressure. This may be done by elevating the combustion zone above the reactor coke bed. For a 50 p.s.i.g. operation, an elevation of the top of the burner of about 150 feet above the reactor coke bed Will allow suflicient pressures to be built up in standpipe 23 and 24 such that the combustion zone can be operated at about atmospheric pressures.

The following table, giving preferred ranges of operating conditions and a specific example for the process illustrated, will further elucidate this invention:

Preferred Example Range Recycle Cut Point, F 500 to 900 700 Feed Rate to Coker (6), lb. oil/hr./lb. coke in reactor to 1.0 0.7 Pressure, outlet of coker, p.s.i. 25 to 400 50 Temperature, F., Ooken- 850 to 1, 100 900 Strlpper 1, 000 to 1,200 1,025 .Burner 1,000 to 1,800 l, 500 CpkeE1 Cireulation'rate to burner; lbs. coke/lb.

Based on coke to reactor 6 5 to 15 Based on coke to stripper l1 1 to 5 1 2 Steam rate to stripper, lbs. steam/hr./lb. coke m stripper 0. 01 to 0. 0.08

1 This rate is based on providing all of the heat to reactor 6 by hot coke from vessel 11. The 1500 solids go only to Vessel 11 in 2/1 coke/oil ratio based on fresh 011 feed to the process.

4 For the conditions specified in the above example, the following products may be obtained from the coking of a 700 F.+ Coleville reduced crude (15 weight percent Conradson carbon):

Light gas, C vol. percent 13 Naphtha, C.;, 430 F., vol. percent 30 Heating oil, 430-700 F., vol. percent 28 Aromatic tar, 700 F.+, vol. percent 20 Coke, wt. percent 19 In many instances wherein an oil is coked by contact with heat carrying solids, it has been found advisable to use a transfer line reactor to carry out the coking process. In such a process, the oil is introduced into an elongated conduit containing finely divided solids, such as coke of 0-1000 microns in size, having a temperature of 850- 1600 F., and conveyed through the conduit along with the solids at velocities above 20 feet per second, e.g., 60 ft./ sec. The oil is pyrolytically converted upon contact with the solids in the transfer line in a manner similar to coking in a fluidized bed of solids. Accordingly, it will be appreciated by those skilled in the art that a transfer line reactor or coker may be appropriately substituted, in certain instances, for the fluidized solids bed cokers described in conjunction with the process of the present invention. Specifically, with reference to the drawing, a transfer line coker may be substituted for the fluid bed coker 6, described above.

It should be mentioned that there are advantages in carrying out the present invention using relatively porous solids, such as silica gel, steam activated carbon or kieselguhr, as the heat carrying media. Such solids will have an adsorptive effect which will reduce the reactor pressure required to secure a given product endpoint and also will decrease, because of their higher surface area per volume, the amount of solids that must be circulated between the primary coking and secondary coking or stripping vessels. Also, it is known that materials such as steam activated carbon have a catalytic effect on the cracking reaction.

If an inert solid, such as particulate kieselguhr, be used, then the carbon deposited on its during the coking would be substantially removed during the combustion step to regenerate it. If porous carbonaceous solids be used, then they may be continuously regenerated by steam, as by a water gas or gasification reaction, to increase their surface area and activity, as is known by the art.

Considerable savings may be effected by preheating the feed injected into the fluid coking vessel. From a practical standpoint, the maximum feed preheat that may be expected from separators 3 and 52 is about 750-800 F. By preheating this feed to a temperature in the range of about 900-950 F., savings may be made on the cost of compression or air for the burner vessel as the heat load in the coking vessel is reduced. Thus it is beneficial to heat the contents of line 5 up to about 900950 F. in a high pressure coil in a manner well known by the art.

It can be readily seen that the process of this invention has several advantages over conventional fluid coking proceses in that smaller vessels can be used for a given feed rate because of the higher pressures; higher thermal cracking severity is available where needed to crack the aromatic and more refractory feed components; recycling of products to produce a given end point material is eliminated and there is a lower vapor cracking time in the reactor resulting in improved product distribution.

Having described the invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. In a hydrocarbon oil upgrading process wherein a heavy highly aromatic oil is injected into a coking zone containing a fluidized bed of high temperature inert particulate solids, wherein a portion of said solids is continuously circulated to an external heating zone and back to maintain said bed at a coking temperature in the range of 850 to 1100 E, wherein coke produced in the process is removed as product, wherein vapors are removed from said coking zone and said vapors are separated in the separation zone to obtain product boiling below a specified endpoint in the range of 500 to 900 F., the improved method for obtaining maximum production of middle distillates while substantially eliminating the necessity for recycling the higher boiling portions of said vapors, which comprises operating said coking zone under a pressure in a range of 25 to 400 p.s.i.g. sufiicient to maintain substantially all hydrocarbons boiling above said endpoint as liquids at said coking temperature, passing said portion of solids to an external stripping zone along with liquid hydrocarbons adhering thereto prior to transferring said portion to said heating zone, passing a gasiform medium upwardly through said stripping zone to maintain solids therein in a relatively dense fluidized mass, maintaining said mass at a higher temperature in the range of l000 to 1200 F. than said reaction temperature, withdrawing eflluent from the upper portion of said mass recovering from said effluent a heavy tar boiling above said specified endpoint and passing the remainder of said eftluent to said separation zone.

2. The method of claim 1 wherein a petroleum oil is admixed with said vapors to quench said vapors and preheat said petroleum oil and bottoms from said separation zone boiling above said endpoint comprising said heavy hydrocarbon oil.

3. The process of claim 2 wherein said petroleum oil is a highly aromatic whole crude.

4. A method of processing petroleum oils comprising injecting a high boiling oil into a coking zone having a.

pressure in a range of 25 to 400 p.s.i.g. sufiicient to maintain substantially all hydrocarbons boiling above an endpoint in the range of 500900 F. in the liquid phase and containing finely divided coke having a temperature in the range of 8501100 F., withdrawing vaporous effiuent from said coking zone as product, circulating a portion of said finely divided coke along with adhering liquid hydrocarbons to an external stripping zone containing a mobilized relatively dense mass of particulate coke with a temperature in the range of 1000-1200 F., passing a fiuidizing gas upwardly through said stripping zone countercurrent to said particulate coke to remove liquid hydrocarbons adhering thereto, removing vapors from said stripping zone, removing a heavy high aromatic fraction boiling above 700 F. from said stripping zone vapors, commingling the remainder of said vapors with the vaporous efiluent of said coking zone, passing particulate coke from the lower portion of said stripping zone to a combustion zone and returning coke particles with a temperature in the range of 1000l800 F. from said combustion zone to said stripping zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,391,336 Ogorzaly Dec. 18, 1945 2,485,315 Rex et al. Oct. 18, 1949 2,490,993 Borcherding Dec. 13, 1949 2,554,263 Nelson May 22, 1951 2,579,398 Roetheli Dec. 18, 1951 2,598,058 Hunter May 27, 1952 2,655,464 Brown et a1 Oct. 13, 1953 2,707,702 Watson May 3, 1955 2,731,508 Jahnig et a1. .a Jan. 17, 1956 

1. IN A HYDROCARBON OIL UPGRADING PROCESS WHEREIN A HEAVY HIGHLY AROMATIC OIL IS INJECTED INTO A COKING ZONE CONTAINING A FLUIDIZED BED OF HIGH TEMPERATURE INERT PARTICULATE SOLIDS, WHEREIN A PORTION OF SAID SOLIDS IS CONTINUOUSLY CIRCULATED TO AN EXTERNAL HEATING ZONE AND BACK TO MAINTAIN SAID BED AT A COKING TEMPERATURE IN THE RANGE OF 850* TO 1100*F., WHEREIN COKE PRODUCED IN THE PROCESS IS REMOVED AS PRODCT, WHEREIN VAPORES ARE REMOVED FROM SAID COKING ZONE AND SAID VAPORS ARE SEPARATED IN THE SEPARATION ZONE TO OBTAIN PRODUCT BOILING BELOW A SPECIFIED ENDPOINT IN THE RANGE OF 500* TO 900*F., THE IMPROVED METHOD FOR OBTAINING MAXIMUM PRODUCTION OF MIDDLE DISTILLATES WHILE SUBSTANTIALLY ELIMINATINHG THE NECESSITY FOR RECYCLING THE HIGHER BOILING PORTIONS OF SAID VAPORS, WHICH COMPRISES OPERATING SAID COKING ZONE UNDER A PRESSURE IN A RANGE OF 25 TO 400 P.S.I.G. SUFFICIENT TO MAINTAIN SUBSTANTIALLY ALL HYDROCARBONS BOILING ABOVE SAID ENDPOINT AS LIQUIDS AT SAID COKING TEMPERATURE, PASSING SAID PORTION OF SOLIDS TO AN EXTERNAL STRIPPING ZONE ALONG WITH LIQUID HYDROCARBON ADHERING THRETO PRIOR TO TRANSFERRING SAID PORTION TO SAID HEATING ZONE, PASSING A GASIFORM MEDIUM UPWARDLY THROUGH SAID STRIPPING ZONE TO MAINTAIN SOLIDS THEREIN IN A RELATIVELY DENSE FLUIDIZED MASS, MAINTAINING SAID MASS AT A HIGHER TEMPERATURE IN THE RANGE OF 100* TO 1200*F. THAN SAID REACTION TEMPERATURE, WITHDRAWING EFFUENT FROM THE UPPER PORTION OF SAID MASS RECOVERING FROM SAID EFFUENT A HEAVY TAR BOILING ABOVE SAID SPECIFIED ENDPOINT AND PASSING THE REMAINDER OF SAID EFFUENT TO SAID SEPARATION ZONE. 